/*
 * #%L
 * Netarchivesuite - common
 * %%
 * Copyright (C) 2005 - 2018 The Royal Danish Library, 
 *             the National Library of France and the Austrian National Library.
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 2.1 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 * 
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * <http://www.gnu.org/licenses/lgpl-2.1.html>.
 * #L%
 */
package dk.netarkivet.common.distribute;

import java.util.Calendar;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.Destination;
import javax.jms.ExceptionListener;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageConsumer;
import javax.jms.MessageListener;
import javax.jms.MessageProducer;
import javax.jms.ObjectMessage;
import javax.jms.Queue;
import javax.jms.QueueBrowser;
import javax.jms.QueueSession;
import javax.jms.Session;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import dk.netarkivet.common.CommonSettings;
import dk.netarkivet.common.exceptions.ArgumentNotValid;
import dk.netarkivet.common.exceptions.IOFailure;
import dk.netarkivet.common.exceptions.PermissionDenied;
import dk.netarkivet.common.utils.CleanupHook;
import dk.netarkivet.common.utils.CleanupIF;
import dk.netarkivet.common.utils.Settings;
import dk.netarkivet.common.utils.TimeUtils;

/**
 * Handles the communication with a JMS broker. Note on Thread-safety: the methods and fields of JMSConnection are not
 * accessed by multiple threads (though JMSConnection itself creates threads). Thus no synchronization is needed on
 * methods and fields of JMSConnection. A shutdown hook is also added, which closes the connection. Class JMSConnection
 * is now also a exceptionhandler for the JMS Connections
 */
public abstract class JMSConnection implements ExceptionListener, CleanupIF {

    /** The log. */
    private static final Logger log = LoggerFactory.getLogger(JMSConnection.class);

    /** Separator used in the consumer key. Separates the ChannelName from the MessageListener.toString(). */
    protected static final String CONSUMER_KEY_SEPARATOR = "##";

    /** The number to times to (re)try whenever a JMSException is thrown. */
    static final int JMS_MAXTRIES = Settings.getInt(CommonSettings.JMS_BROKER_RETRIES);

    /** The JMS Connection. */
    protected Connection connection;

    /**
     * The Session handling messages sent to / received from the NetarchiveSuite queues and topics.
     */
    protected Session session;

    /** Map for caching message producers. */
    protected final Map<String, MessageProducer> producers = Collections
            .synchronizedMap(new HashMap<String, MessageProducer>());

    /** Map for caching message consumers (topic-subscribers and queue-receivers). */
    protected final Map<String, MessageConsumer> consumers = Collections
            .synchronizedMap(new HashMap<String, MessageConsumer>());

    /** Map for caching message listeners (topic-subscribers and queue-receivers). */
    protected final Map<String, MessageListener> listeners = Collections
            .synchronizedMap(new HashMap<String, MessageListener>());

    /**
     * Lock for the connection. Locked for read on adding/removing listeners and sending messages. Locked for write when
     * connection, releasing and reconnecting.
     */
    protected final ReentrantReadWriteLock connectionLock = new ReentrantReadWriteLock();

    /** Shutdown hook that closes the JMS connection. */
    protected Thread closeHook;

    /** Singleton pattern is be used for this class. This is the one and only instance. */
    protected static JMSConnection instance;

    /**
     * Should be implemented according to a specific JMS broker.
     *
     * @return QueueConnectionFactory
     * @throws JMSException If unable to get QueueConnectionFactory
     */
    protected abstract ConnectionFactory getConnectionFactory() throws JMSException;

    /**
     * Should be implemented according to a specific JMS broker.
     *
     * @param destinationName the name of the wanted Queue
     * @return The destination. Note that the implementation should make sure that this is a Queue or a Topic, as
     * required by the NetarchiveSuite design. {@link Channels#isTopic(String)}
     * @throws JMSException If unable to get a destination.
     */
    protected abstract Destination getDestination(String destinationName) throws JMSException;

    /**
     * Exceptionhandler for the JMSConnection. Implemented according to a specific JMS broker. Should try to reconnect
     * if at all possible.
     *
     * @param e a JMSException
     */
    public abstract void onException(JMSException e);

    /** Class constructor. */
    protected JMSConnection() {
    }

    /**
     * Initializes the JMS connection. Creates and starts connection and session. Adds a shutdown hook that closes down
     * JMSConnection. Adds this object as ExceptionListener for the connection.
     *
     * @throws IOFailure if initialization fails.
     */
    protected void initConnection() throws IOFailure {
        log.debug("Initializing a JMS connection {}", getClass().getName());

        connectionLock.writeLock().lock();
        try {
            int tries = 0;
            JMSException lastException = null;
            boolean operationSuccessful = false;
            while (!operationSuccessful && tries < JMS_MAXTRIES) {
                ++tries;
                try {
                    establishConnectionAndSession();
                    operationSuccessful = true;
                } catch (JMSException e) {
                    closeConnection();
                    log.debug("Connect failed (try {})", tries, e);
                    lastException = e;
                    if (tries < JMS_MAXTRIES) {
                        log.debug("Will sleep a while before trying to connect again");
                        TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                    }
                }
            }
            if (!operationSuccessful) {
                log.warn("Could not initialize JMS connection {}", getClass(), lastException);
                cleanup();
                throw new IOFailure("Could not initialize JMS connection " + getClass(), lastException);
            }
            closeHook = new CleanupHook(this);
            Runtime.getRuntime().addShutdownHook(closeHook);
        } finally {
            connectionLock.writeLock().unlock();
        }
    }

    /**
     * Submit an object to the destination queue. This method shouldn't be overridden. Override the method sendMessage
     * to change functionality.
     *
     * @param msg The NetarkivetMessage to send to the destination queue (null not allowed)
     * @throws ArgumentNotValid if nMsg is null.
     * @throws IOFailure if the operation failed.
     */
    public void send(NetarkivetMessage msg) {
        ArgumentNotValid.checkNotNull(msg, "msg");
        log.trace("Sending message ({}) to {}", msg.toString(), msg.getTo());
        sendMessage(msg, msg.getTo());
    }

    /**
     * Sends a message msg to the channel defined by the parameter to - NOT the channel defined in the message.
     *
     * @param msg Message to be sent
     * @param to The destination channel
     */
    public final void resend(NetarkivetMessage msg, ChannelID to) {
        ArgumentNotValid.checkNotNull(msg, "msg");
        ArgumentNotValid.checkNotNull(to, "to");
        log.trace("Resending message ({}) to {}", msg.toString(), to.getName());
        sendMessage(msg, to);
    }

    /**
     * Submit an object to the reply queue.
     *
     * @param msg The NetarkivetMessage to send to the reply queue (null not allowed)
     * @throws ArgumentNotValid if nMsg is null.
     * @throws PermissionDenied if message nMsg has not been sent yet.
     * @throws IOFailure if unable to reply.
     */
    public final void reply(NetarkivetMessage msg) {
        ArgumentNotValid.checkNotNull(msg, "msg");
        log.trace("Reply on message ({}) to {}", msg.toString(), msg.getReplyTo().getName());
        if (!msg.hasBeenSent()) {
            throw new PermissionDenied("Message has not been sent yet");
        }
        sendMessage(msg, msg.getReplyTo());
    }

    /**
     * Method adds a listener to the given queue or topic.
     *
     * @param mq the messagequeue to listen to
     * @param ml the messagelistener
     * @throws IOFailure if the operation failed.
     */
    public void setListener(ChannelID mq, MessageListener ml) throws IOFailure {
        ArgumentNotValid.checkNotNull(mq, "ChannelID mq");
        ArgumentNotValid.checkNotNull(ml, "MessageListener ml");
        setListener(mq.getName(), ml);
    }

    /**
     * Removes the specified MessageListener from the given queue or topic.
     *
     * @param mq the given queue or topic
     * @param ml a messagelistener
     * @throws IOFailure On network trouble
     */
    public void removeListener(ChannelID mq, MessageListener ml) throws IOFailure {
        ArgumentNotValid.checkNotNull(mq, "ChannelID mq");
        ArgumentNotValid.checkNotNull(ml, "MessageListener ml");
        removeListener(ml, mq.getName());
    }

    /**
     * Creates a QueueBrowser object to peek at the messages on the specified queue.
     *
     * @param queueID The ChannelID for a specified queue.
     * @return A new QueueBrowser instance with access to the specified queue
     * @throws JMSException If unable to create the specified queue browser
     */
    public QueueBrowser createQueueBrowser(ChannelID queueID) throws JMSException {
        ArgumentNotValid.checkNotNull(queueID, "ChannelID queueID");
        Queue queue = getQueueSession().createQueue(queueID.getName());
        return getQueueSession().createBrowser(queue);
    }
    
    /**
     * Creates a QueueBrowser object to peek at the messages on the specified queue.
     *
     * @param queueID The ChannelID for a specified queue.
     * @param QSession The QueueSession to use.
     * @return A new QueueBrowser instance with access to the specified queue
     * @throws JMSException If unable to create the specified queue browser
     */
    public QueueBrowser createQueueBrowser(ChannelID queueID, QueueSession QSession) throws JMSException {
        ArgumentNotValid.checkNotNull(queueID, "ChannelID queueID");
        ArgumentNotValid.checkNotNull(QSession, "QueueSession QSession");
        Queue queue = QSession.createQueue(queueID.getName());
        return QSession.createBrowser(queue);
    }

    /**
     * Provides a QueueSession instance. Functionality for retrieving a <code>QueueSession</code> object isen't
     * available on the generic <code>JMSConnectionFactory</code>
     *
     * @return A <code>QueueSession</code> object connected to the current JMS broker
     * @throws JMSException Failure to retrieve the <code>QueueBrowser</code> JMS Browser
     */
    public abstract QueueSession getQueueSession() throws JMSException;

    /**
     * Clean up. Remove close connection, remove shutdown hook and null the instance.
     */
    public void cleanup() {
        connectionLock.writeLock().lock();
        try {
            // Remove shutdown hook
            log.info("Starting cleanup");
            try {
                if (closeHook != null) {
                    Runtime.getRuntime().removeShutdownHook(closeHook);
                }
            } catch (IllegalStateException e) {
                // Okay, it just means we are already shutting down.
            }
            closeHook = null;
            // Close session
            closeConnection();
            // Clear list of listeners
            listeners.clear();
            instance = null;
            log.info("Cleanup finished");
        } finally {
            connectionLock.writeLock().unlock();
        }
    }

    /**
     * Close connection, session and listeners. Will ignore trouble, and simply log it.
     */
    private void closeConnection() {
        // Close terminates all pending message received on the
        // connection's session's consumers.
        if (connection != null) { // close connection
            try {
                connection.close();
            } catch (JMSException e) {
                // Just ignore it
                log.warn("Error closing JMS Connection.", e);
            }
        }
        connection = null;
        session = null;
        consumers.clear();
        producers.clear();
    }

    /**
     * Unwraps a NetarkivetMessage from an ObjectMessage.
     *
     * @param msg a javax.jms.ObjectMessage
     * @return a NetarkivetMessage
     * @throws ArgumentNotValid when msg in valid or format of JMS Object message is invalid
     */
    public static NetarkivetMessage unpack(Message msg) throws ArgumentNotValid {
        ArgumentNotValid.checkNotNull(msg, "msg");

        ObjectMessage objMsg;
        try {
            objMsg = (ObjectMessage) msg;
        } catch (ClassCastException e) {
            log.warn("Invalid message type: {}", msg.getClass());
            throw new ArgumentNotValid("Invalid message type: " + msg.getClass());
        }

        NetarkivetMessage netMsg;
        String classname = "Unknown class"; // for error reporting purposes
        try {
            classname = objMsg.getObject().getClass().getName();
            netMsg = (NetarkivetMessage) objMsg.getObject();
            // Note: Id is only updated if the message does not already have an
            // id. On unpack, this means the first time the message is received.

            // FIXME Fix for NAS-2043 doesn't seem to work
            // String randomID = UUID.randomUUID().toString();
            // netMsg.updateId(randomID);

            netMsg.updateId(msg.getJMSMessageID());
        } catch (ClassCastException e) {
            log.warn("Invalid message type: {}", classname, e);
            throw new ArgumentNotValid("Invalid message type: " + classname, e);
        } catch (Exception e) {
            String message = "Message invalid. Unable to unpack message: " + classname;
            log.warn(message, e);
            throw new ArgumentNotValid(message, e);
        }
        log.trace("Unpacked message '{}'", netMsg);
        return netMsg;
    }

    /**
     * Submit an ObjectMessage to the destination channel.
     *
     * @param nMsg the NetarkivetMessage to be wrapped and send as an ObjectMessage
     * @param to the destination channel
     * @throws IOFailure if message failed to be sent.
     */
    protected void sendMessage(NetarkivetMessage nMsg, ChannelID to) throws IOFailure {
        Exception lastException = null;
        boolean operationSuccessful = false;
        int tries = 0;

        while (!operationSuccessful && tries < JMS_MAXTRIES) {
            ++tries;
            try {
                doSend(nMsg, to);
                operationSuccessful = true;
            } catch (JMSException e) {
                log.debug("Send failed (try {})", tries, e);
                lastException = e;
                if (tries < JMS_MAXTRIES) {
                    onException(e);
                    log.debug("Will sleep a while before trying to send again");
                    TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                }
            } catch (Exception e) {
                log.debug("Send failed (try {})", tries, e);
                lastException = e;
                if (tries < JMS_MAXTRIES) {
                    reconnect();
                    log.debug("Will sleep a while before trying to send again");
                    TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                }
            }
        }
        if (!operationSuccessful) {
            log.warn("Send failed", lastException);
            throw new IOFailure("Send failed.", lastException);
        }
    }

    /**
     * Do a reconnect to the JMSbroker. Does absolutely nothing, if already in the process of reconnecting.
     */
    protected void reconnect() {
        if (!connectionLock.writeLock().tryLock()) {
            log.debug("Reconnection already in progress. Do nothing");
            return;
        }
        try {
            log.info("Trying to reconnect to jmsbroker");

            boolean operationSuccessful = false;
            Exception lastException = null;
            int tries = 0;
            while (!operationSuccessful && tries < JMS_MAXTRIES) {
                ++tries;
                try {
                    doReconnect();
                    operationSuccessful = true;
                } catch (Exception e) {
                    lastException = e;
                    log.debug("Reconnect failed (try {})", tries, e);
                    if (tries < JMS_MAXTRIES) {
                        log.debug("Will sleep a while before trying to reconnect again");
                        TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                    }
                }
            }
            if (!operationSuccessful) {
                log.warn("Reconnect to JMS broker failed", lastException);
                closeConnection();
            }
        } finally {
            // Tell everybody, that we are not trying to reconnect any longer
            connectionLock.writeLock().unlock();
        }
    }

    /**
     * Helper method for getting the right producer for a queue or topic.
     *
     * @param queueName The name of the channel
     * @return The producer for that channel. A new one is created, if none exists.
     * @throws JMSException If a new producer cannot be created.
     */
    private MessageProducer getProducer(String queueName) throws JMSException {
        // Check if producer is in cache
        // If it is not, it is created and stored in cache:
        MessageProducer producer = producers.get(queueName);
        if (producer == null) {
            producer = getSession().createProducer(getDestination(queueName));
            producers.put(queueName, producer);
        }
        return producer;
    }

    /**
     * Get the session. Will try reconnecting if session is null.
     *
     * @return The session.
     * @throws IOFailure if no session is available, and reconnect does not help.
     */
    private Session getSession() {
        if (session == null) {
            reconnect();
        }
        if (session == null) {
            throw new IOFailure("Session not available");
        }
        return session;
    }

    /**
     * Helper method for getting the right consumer for a queue or topic, and message listener.
     *
     * @param channelName The name of the channel
     * @param ml The message listener to add as listener to the channel
     * @return The producer for that channel. A new one is created, if none exists.
     * @throws JMSException If a new producer cannot be created.
     */
    private MessageConsumer getConsumer(String channelName, MessageListener ml) throws JMSException {
        String key = getConsumerKey(channelName, ml);
        MessageConsumer consumer = consumers.get(key);
        if (consumer == null) {
            consumer = getSession().createConsumer(getDestination(channelName));
            consumers.put(key, consumer);
            listeners.put(key, ml);
        }
        return consumer;
    }

    /**
     * Generate a consumerkey based on the given channel name and messageListener.
     *
     * @param channel Channel name
     * @param messageListener a messageListener
     * @return the generated consumerkey.
     */
    protected static String getConsumerKey(String channel, MessageListener messageListener) {
        return channel + CONSUMER_KEY_SEPARATOR + messageListener;
    }

    /**
     * Get the channelName embedded in a consumerKey.
     *
     * @param consumerKey a consumerKey
     * @return name of channel embedded in a consumerKey
     */
    private static String getChannelName(String consumerKey) {
        // assumes argument consumerKey was created using metod getConsumerKey()
        return consumerKey.split(CONSUMER_KEY_SEPARATOR)[0];
    }

    /**
     * Helper method to establish one Connection and associated Session.
     *
     * @throws JMSException If some JMS error occurred during the creation of the required JMS connection and session
     */
    private void establishConnectionAndSession() throws JMSException {
        // Establish a queue connection and a session
        connection = getConnectionFactory().createConnection();
        session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
        connection.setExceptionListener(this);
        connection.start();
    }

    /**
     * Sends an ObjectMessage on a queue destination.
     *
     * @param msg the NetarkivetMessage to be wrapped and send as an ObjectMessage.
     * @param to the destination topic.
     * @throws JMSException if message failed to be sent.
     */
    private void doSend(NetarkivetMessage msg, ChannelID to) throws JMSException {
        connectionLock.readLock().lock();
        try {
            ObjectMessage message = getSession().createObjectMessage(msg);
            synchronized (msg) {
                getProducer(to.getName()).send(message);
                // Note: Id is only updated if the message does not already have
                // an id. This ensures that resent messages keep the same ID
                // TODO Is it always OK for resent messages to keep the same ID

                // FIXME Solution for NAS-2043 doesn't work; rolled back
                // String randomID = UUID.randomUUID().toString();
                // msg.updateId(randomID);
                msg.updateId(message.getJMSMessageID());

            }
        } finally {
            connectionLock.readLock().unlock();
        }
        log.trace("Sent message '{}'", msg.toString());
    }

    /**
     * Method adds a listener to the given queue or topic.
     *
     * @param channelName the messagequeue to listen to
     * @param ml the messagelistener
     * @throws IOFailure if the operation failed.
     */
    private void setListener(String channelName, MessageListener ml) {
        log.debug("Adding {} as listener to {}", ml.toString(), channelName);
        String errMsg = "JMS-error - could not add Listener to queue/topic: " + channelName;

        int tries = 0;
        boolean operationSuccessful = false;
        Exception lastException = null;
        while (!operationSuccessful && tries < JMS_MAXTRIES) {
            ++tries;
            try {
                connectionLock.readLock().lock();
                try {
                    getConsumer(channelName, ml).setMessageListener(ml);
                } finally {
                    connectionLock.readLock().unlock();
                }
                operationSuccessful = true;
            } catch (JMSException e) {
                lastException = e;
                log.debug("Set listener failed (try {})", tries, e);
                if (tries < JMS_MAXTRIES) {
                    onException(e);
                    log.debug("Will sleep a while before trying to set listener again");
                    TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                }
            } catch (Exception e) {
                lastException = e;
                log.debug("Set listener failed (try {})", tries, e);
                if (tries < JMS_MAXTRIES) {
                    reconnect();
                    log.debug("Will sleep a while before trying to set listener again");
                    TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
                }
            }
        }

        if (!operationSuccessful) {
            log.warn(errMsg, lastException);
            throw new IOFailure(errMsg, lastException);
        }
    }

    /**
     * Remove a messagelistener from a channel (a queue or a topic).
     *
     * @param ml A specific MessageListener
     * @param channelName a channelname
     */
    private void removeListener(MessageListener ml, String channelName) {
        String errMsg = "JMS-error - could not remove Listener from queue/topic: " + channelName;
        int tries = 0;
        Exception lastException = null;
        boolean operationSuccessful = false;

        log.info("Removing listener from channel '{}'", channelName);
        while (!operationSuccessful && tries < JMS_MAXTRIES) {
            try {
                ++tries;
                connectionLock.readLock().lock();
                try {
                    MessageConsumer messageConsumer = getConsumer(channelName, ml);
                    messageConsumer.close();
                    consumers.remove(getConsumerKey(channelName, ml));
                    listeners.remove(getConsumerKey(channelName, ml));
                } finally {
                    connectionLock.readLock().unlock();
                }
                operationSuccessful = true;
            } catch (JMSException e) {
                lastException = e;
                log.debug("Remove listener failed (try {})", tries, e);
                onException(e);
                log.debug("Will and sleep a while before trying to remove listener again");
                TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
            } catch (Exception e) {
                lastException = e;
                log.debug("Remove  listener failed (try {})", tries, e);
                reconnect();
                log.debug("Will and sleep a while before trying to remove listener again");
                TimeUtils.exponentialBackoffSleep(tries, Calendar.MINUTE);
            }
        }
        if (!operationSuccessful) {
            log.warn(errMsg, lastException);
            throw new IOFailure(errMsg, lastException);
        }
    }

    /**
     * Reconnect to JMSBroker and reestablish session. Resets senders and publishers.
     *
     * @throws JMSException If unable to reconnect to JMSBroker and/or reestablish sessions
     */
    private void doReconnect() throws JMSException {
        closeConnection();
        establishConnectionAndSession();
        // Add listeners already stored in the consumers map
        log.debug("Re-add listeners");
        for (Map.Entry<String, MessageListener> listener : listeners.entrySet()) {
            setListener(getChannelName(listener.getKey()), listener.getValue());
        }
        log.info("Reconnect successful");
    }

}